Insights
J.S. Held Releases Insights on Risks & Opportunities Expected to Impact Organizations in 2025
Read MoreWhen arriving at the scene of a vehicular accident, some of the critical evidence available to an investigator is the physical evidence generated during the collision and the rest positions of the vehicles. The job of an accident reconstructionist is to analyze that physical evidence and determine what the vehicles were doing prior to and after impact using the principles of physics and dynamics. To better understand the dynamics of vehicles, extensive research and testing has been performed by our consultants to determine the speed, handling, acceleration, and braking properties of not only passenger vehicles, but also heavy trucks, motorcycles, bicycles, and other operator controlled vehicles. This research and testing provides valuable insight into the capabilities of vehicles and how they operate under, at, or beyond their limits.
The following peer-reviewed, scientific publications demonstrate our expertise in vehicle testing, handling, and driver capabilities.
This paper evaluates event data from the Sensing and Diagnostic Module (SDM) of a sedan during high speed yaw testing involving tires that were intact and tires that had the tread removed. The authors examine the dynamic effect of high sideslip angles and changes to tire rolling radius, as a result of a tread separation, as it pertains to the accuracy of Event Data Recorder (EDR) reported vehicle speed.
This paper presents a comprehensive analysis of the performance of Event Data Recorders (EDRs) found in the Airbag Control Modules (ACMs), as tested in support of the National Highway Traffic Safety Administration’s Frontal Oblique Offset Program. In addition to analyzing data from a high severity oblique frontal impact test in which the vehicle was struck by a moving deformable barrier, the authors also examine the results of EDR data downloaded from two 2015 model year Toyota Highlanders, and the results of EDR reported change in velocity (delta-v), to vehicle mounted accelerometers and reference instrumentation.
In low speed collisions (under 15 mph) that involve a heavy truck impacting the rear of a passenger vehicle, it is likely that the front bumper of the heavy truck will override the rear bumper beam of the passenger vehicle, creating an override/underride impact configuration. The authors of this paper discuss three low speed impact tests that were conducted to expand the available data set for passenger vehicle dynamics and damage assessment for low speed override/underride rear impacts to passenger vehicles.
The Critical Speed Formula has long been used by accident reconstructionists for estimating a vehicle’s speed at the beginning of yaw tire marks. This paper presents yaw testing of vehicles with tread removed from tires at various locations. The research here extends the Critical Speed Formula to include yawing vehicles following a tread detachment event and analyzes the inputs and guidelines for the use of the formula for these tread detachment scenarios.
A three-wheeled vehicle has handling and stability characteristics that differ both from two-wheeled motorcycles and from four-wheeled vehicles. The data reported in this paper will enable accident reconstructionists to consider these different characteristics when analyzing a three-wheeled motorcycle operator’s ability to brake or swerve to avoid a crash.
Several papers published over the past 25 years examine the acceleration of heavy trucks, providing a large data set that measures the speed, distance, and time of the vehicles during acceleration testing. The data is presented in tabular or graphical formats. There are approximately eight relevant papers with a total of 268 acceleration tests performed, spanning many years. This paper reviews all the available published literature and summarizes the relevant data in a comprehensive list of accelerations for different heavy truck configurations, providing a valuable resource to the accident reconstruction field.
In this study of the deceleration rates of vehicles whose tires were disabled, the magnitude of the deceleration was measured for different phases of 29 high speed tire tread separation and air loss tests. It was found that each disablement event was made of one or more phases. In all, six different phases were identified. These deceleration rates can assist in reconstructing the speed of a vehicle involved in an accident following a tire disablement.
Calculating the speed of a yawing and braked vehicle often requires an estimate of the vehicle deceleration. When there is an impact and the resulting yaw velocity is high, the rotational velocity can have a meaningful effect on the deceleration. High yaw velocities can also cause steering angles to develop at the front tires, which also can affect the deceleration. This paper explores the influence of high rotational energies and impact-induced steering on the deceleration experienced by a vehicle following an impact.
This paper focuses on the practical use of striation evidence for accident reconstruction purposes. The authors explore the sensitivity and uncertainty of an equation that related tire mark striation angle to longitudinal tire slip, which is the mathematical definition of braking. This equation can be used to quantify the driver’s braking input based on the physical evidence. Braking input levels will affect the speed of a yawing vehicle and quantifying the amount of braking can increase the accuracy of a speed analysis.
In this article, the differences in the mechanism in which tire mark striations are deposited and the interpretation of this evidence are explored. This paper focuses on discussions about striations in the literature and the relationship between tire mark striations and tire forces. To further confirm that relationship between tire force and striation direction, a vehicle dynamics simulation software package was used to compare simulated tire force direction with predicted striation direction.
Tire tread separation events, a category of tire disablements, can be sub-categorized into two main types of separations: full or partial. This study reports the results of 25 full and partial tire tread separation tests, conducted with a variety of vehicles at highway speeds. This article adds to the literature a number of partial separations across a wider selection of vehicles and also compares the results to full tread separation testing performed with the same vehicles.
Accurately reconstructing the speed of a yawing and braking vehicle requires an estimate of the varying rates at which the vehicle decelerated. In a crash reconstruction context, simulation is not always necessary, and a more simple analysis can yield the rate at which a vehicle decelerated due to tire forces along a known path. The primary objective of this paper will be to calculate a yawing and braking vehicle's translational speed at the beginning of tire mark evidence using a calculated deceleration rate. This paper explores the accuracy of several approaches to making this calculation.
A fatal accident involving trailer swing indicated there there is some disagreement within the accident reconstruction industry as to what effects trailer anti-lock brake systems have on the stopping performance, dynamic performance/handling of the trailer, and resultant skid marks left on the roadway. Full-scale testing was conducted on a tractor-trailer unit which was equipped with anti-lock brakes on both the tractor and trailer. Results showed the types of marks left by tires both with and without anti-lock brakes. The tests, discussed in this paper, also provided qualitative indications as to the effect of locked trailer tires on trailer swing.
This paper presents equations that relate the orientation and spacing of yaw mark striations to the vehicle braking and steering levels present at the time the striations were deposited. These equations, thus, provide a link between physical evidence deposited on a roadway during a crash (the tire mark striations) and actions taken by the driver during that crash (steering and braking inputs).
Accidents involving heavy trucks turning left across travel lanes of a roadway are common subjects of investigation in the field of accident reconstruction. This paper will investigate the longitudinal and lateral accelerations of heavy trucks during small, medium, and large radius turns and analyze peak and average lateral accelerations as they relate to turn radius and vehicle speeds. This paper was selected to appear in SAE International’s Journal of Advances in Current Practices in Mobility, 2020.
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